The present invention is concerned with the management of temperature of a mould tool. More specifically the present invention is concerned with management of the temperature of a mould tool which utilises fluid heating and cooling, in particular to reduce the thermal losses of the edge zones of the mould tool.
Fluid heating of layered mould tools is known, in particular from the applicant's earlier application published as WO 2013/021195. In this document, fluid-based heating of the mould tool face in order to control the curing properties of the workpiece is discussed, whilst the control circuitry and delicate componentry of the mould tool is protected from excessive temperatures through the tool's layered structure. When this type of heating is used it is desirable to limit the amount of heat lost to the surrounding environment through the mould tool.
Zone control of tool temperature is also known, in particular from the applicant's earlier application published as WO 2011/048365. In this document, heating and cooling means are independently associated with each tool “pixel”—which may be defined as described below.
In one embodiment of WO 2011/048365 each heated/cooled tool pixel has an independent in-line heater/cooler associated therewith, comprising an internal channel in each tool pixel below the tool surface through which a heating/cooling fluid is passed. The pixels are arranged to tessellate to form the tool surface at their upper surface.
Heat loss can be characterized in the three axes of the mould tool: X, Y and Z, (X and Y in the lateral direction, and Z in the vertical direction). Mould tools may be designed so that the predominant direction for heat transfer is towards the mould face (i.e. +Z), to mitigate heat losses in the −Z direction. However, the region of greatest heat lost from the tool is at its periphery (in the lateral directions X, Y), generally termed the mould tool edge zone, where a greater proportion of the tool is exposed to ambient air. Thus temperature control of the mould tool edge zone can be difficult to manage due to these losses.
Whilst it is possible to operate the heating means associated with the pixels located in the edge zone at a higher temperature than those pixels located in the centre of the mould tool, to account for these losses, this clearly is not an efficient solution and is unworkable when a maximum temperature is required across the entire mould face.
The importance of good temperature management of the tool surface in the tool edge zones is evident, as commonly parts need the tightest tolerances at their edges, which form interfaces with other parts. Furthermore parts may commonly have their deepest section at their edges, to provide the necessary structural rigidity of the part to be formed, examples include the “tray-like” castings for mobile phone, laptop computer or tablet computer cases.
It is an aim of the present invention to overcome or at least mitigate one or more of the above problems.